Metallurgical process



Sept 10, 1957 R. S. HOLMES ET AL METALLURGICAL PROCESS Filed March 11, 1952 INVENTORS RAYMOND 6. HOLMES BY u/vcouv r WORK AGENT United States Patent Ofiice 2,805,624 Patented Sept. 10, 1957 METALLURGICAL PROCESS Raymond S. Holmes, Alton, Ill., and Lincoln T. Work,

Maplewood, N. J., assignors to Olin Ninthxeson Chenncal Corporation, a corporation of Virginia Application March 11, 1952, ScrialNoZflSfldB 6 Claims. (Cl. 1c2-92.5)

This invention relates generally to a method for form- ;ing briquettes from particles of iron :and more particularly to a method for making novel projectiles for ammunition cartridges.

Articles formed by pressing and sintering iron powders have been proposed heretofore. Many types of articles such as gears, bearings, rifting bands, bushings, etc. have been made in this way and it has been the custom, heretofore, in some instances, to impregnate the relatively porous articles with oils or other lubricating materials. These products have been made of relatively low density by pressing iron powders coated with a suitable binder into compacts which are sintered at relatively high temperatures to form a briquette. Articles having a some- ,What higher density have been obtained by again press- .ingsuch briquettes at a higher pressure and again sinter- .ing, as disclosed by Tormyn in U. S. 2,299,192 and Whitney in U. S. 2,411,073. However, the densities obtained even after such second pressing and sintering steps were materially lower than that of solid iron. It has also been proposed to manufacture projectiles for ammunition cartridges and shells from iron powders but these projectiles have had a porous structure and a low density, for in- .stance often as low as about 4.7 grams per milliliter. Projectiles of this type can not be substituted for lead projectiles inmost ammunition cartridges and are suitable only for shortrange target practice. Some attempts have been made to improve the density ofthe porous iron projectile by impregnating and coating it with lead but such a projectile is of little value as a substitute for lead projectiles because the primary purpose for searching for a suitable substitute has been to relieve the critical shortage of relatively pure lead, particularly during a period of War. Like projectiles formed by swaging cut lengths of iron rod and wire, the heretofore proposed projectiles formed from iron powders have had the additional disadvantage of excessively Wearing or eroding the ri-fiing of the gun barrel thus materially shortening the useable life thereof.

.It is therefore an object of this invention-to provide aprocess for forming a novel briquette from particles of iron. It is another object of this invention to provide an improved process for forming a substantially non-porous briquette from particles .of iron. It is another object of this invention to provide an improved process for forming a substantially non-porous briquette from particles of iron. Still another object of this invention is to provide a method for making a briquette from particles of iron which is adapted for use as a projectile for ammunition cartridges and shells. It is a further object of this invention to provide an improved iron projectile. A still further objectof this invention is to provide a substantially non-porous projectile for ammunition cartridges formed from particles of iron.

In the drawing:

Figure 1 is a longitudinal sectional view of a die for forming a compact by means of compressionin the manufacture of a projectile;

Figure 2 is a longitudinal sectional view of a die for shaping projectiles; and

Figure 3 is a perspective view of the novel projectile made in accordance with the process of this invention.

The foregoing objects as well as others which will become apparent from the following description are accomplished in accordance with this invention, generally speaking, by providing .a method for making a substantially non-porous briquette from substantially spherical paricles of iron. More specifically, this invention contemplates a method for forming a briquette adapted for use as a projectile from mixtures of substantially spherical particles of iron having comparatively large dimensions and. particles of iron having lesser dimensions. A briquette can be formed in accordance with this invention by a process wherein substantially spherical particles of iron having a substantially smooth surface are coated with smaller iron particles while wet with a suitable binder, pressed into a compact While confined in a suitable die and sintered. Maximum density is then obtained by pressing the briquette to final shape and again sintering. The last two steps of shaping and sintering materially increasethe density of the briquette.

The product formed by the process disclosed by HancoX, Tuer and Stutzman in U. ,8. Patent 2,544,678 has been found to be particularly advantageous for the comparatively large sized iron particles although substantially spherical particles of iron formed by other processes can be utilized. It is preferred that the larger particles be substantially spherical. By substantially spherical particles of iron is meant spherical, nearly spherical, tearshaped or ovoid particles of iron. The greatest dimension of .the larger iron particles should preferably be not more than will permit free flow of the mixture or uni form filling of the mold cavity but can be as small as about 300.to 400 microns. For instance, spherical particles as large as about 0.2 inch and larger can be utilized in some designs. Iron powders produced by known electrolytic, chemical reduction, grinding or other processes can be utilized for the smaller particles. For instance, powders having a granulation of about microns or less may be used in forming articles having dimensions approximating those of a caliber .30 projectile, but particles ofiron having a particle size of about 40 microns or less are preferred. In general, the larger the article to be manufactured, the larger the particles of iron powder and spheres permissible. Projectiles having a composition of percent by weight of comparatively large particles of iron and about 40 to approximately 20 percent by weight smaller particles of iron have particularly advantageous properties. Heretofore, it has been found in practice that only electrolytically produced iron powders could be used to produce the most non-porous briquettes of the prior art, but it is to be noted that, in accordance with this invention, iron powders produced by methods other than electrolytic depositioncan be utilized.

It has been found that projectiles made in accordance with the process of this invention, unlike prior projectiles formed from iron, have a density which approaches that of pure iron. For example, projectiles having a density of spherical particles of iron coated with smaller particles of iron. In comparison, the density of pure iron is about 7.86 grams per milliliter.

The projectiles of this invention probably because of the structure of their surface erode the gun barrel less than prior art iron projectiles. It is believed, although not as yet definitely determined, that this advantageous property is due at least partially to the heterogeneous .riiiing of the barrel than thesurface of heretofore known projectiles. Deformation of the larger particles of iron, of course, is dependent upon the hardness thereof. Preferably, the hardness of these particles'should be less than'the hardness of the smaller particles and have a Vickers or Diamond Pyramid hardness of about 220 or less. The hardness values herein referred to were determined by employing a 136 degree square base diamond indenter and applying a load of one kilogram on a Tukon tester for twenty seconds as described in the October 1945 Engineering Achievement Issue of Materials and Methods in the article entitled Microhardness testing of materials:: 'Knoop indenter adapted in the Tukon hardness tester, by Vincent Lysaght, and as described in the February 1947 issue of Modern Machine Shop in the article entitled Microhardness testing of small tools, by G. E. Shubrooks. A similar hardness value is obtained with a Vickers instrument following the procedure described in the 1948 edition, pp. 95 to 96, of Metals Handbook published by the American Society for Metals. Briquettes formed in accordance with this invention are also more easily removed from the die after pressing which is attributed to the heterogeneous structure of the surface thereof.

Still other advantageous properties have been found inherent with projectiles made in accordance with this invention. For instance, compacts having particles of iron coated with smaller iron particles shrink less during sintering than compacts formed entirely from iron powder. This is of utmost importance in the manufacture of projectiles as only a very small variation in dimensions can be tolerated. The density of the raw material of thisinvention, i. e. substantially spherical particles of iron coated with smaller particles of iron, is higher than that of powdered iron so smaller volumes thereof can be used to form the projectile and shorter plunger strokes can be used to press the compact which facilitates production thereof. In addition, the compact of this invention formed by pressing and before sintering has been found to have good green strength and can be handled on a mass production basis.

In order to more fully describe and to further clarify this invention, the following is a description of one embodiment thereof with reference to the accompanying drawing:

In making a caliber .30 projectile, about 30 parts by weight electrolytic iron powder (referred to hereinafter in this example as iron powder) having a granulation of less than 44 microns are coated with a liquid containing about one part paraflin, about one part hydrogenated cottonseed oil dissolved in about 10 parts carbon tetrachloride by stirring the iron powder and liquid together in suitable tank provided with a paddle type agitator. The thus coated iron powder is subsequently mixed in a kneader type mixer with about 70 parts by weight iron shot made in accordance with theprocess disclosed by Hancox, et al. in U. S. Patent 2,544,678 and substantially fully annealed to a Diamond Pyramid hardness of about 60150 and having a maximum particle size of about 0.07 inch or about 1800 microns in diameter. This mixing treatment is continued for about 30 minutes after which the mixture of iron shot and iron powder is heated to about 100 C. for about one-half hour to re move the carbon tetrachloride. The dried iron shotiron powder mixture is transferred to a ball mill and tumbled for about one-half to one hour or until a sub stantially uniform coating of the iron powder clings to the surface of each of the iron shot, Coating of the shot with the powder is expedited by placing a few steel balls about five-eighths inch indiarneter in the ball mill withtlre iron shot-ironpowder mixture. e v

Referring now to the drawing, the iron shot coated with iron powder is fed into a one-piece die 4 shown in Figure l. The cavity 5 in die 4 having a diameter approximately equal to the diameter of a caliber .30 projectile is filled to a volume of about 1.6 times as great as the volume of a caliber .30 projectile. The apparent density of the coated iron shot is about 4.25 to 4.50 grams per milliliter. Pressure is then applied and plunger 1 -moved downward through die 4 while plunger 2 is simultaneously moved upward confining the coated iron shot therebetween. A final pressure of about tons per square inch is used to reduce the volume of the coated shot and to form a compact having a density within the range of about 6.6 to about 7.1 grams per milliliter. The

compact is removed from the die 4 by withdrawing plunger 1 and forcing plunger 2 and ejector pin 3 upwardly until the compact has cleared the upper surface of die 4. The end portion of thecompact enclosed in the cavity designated by its two component parts 11 and 12 of plunger 2 is removed therefrom by continuing the upward movement of ejector pin 3 while holding plunger 2 stationary. The compact is then delivered to a conventional sintering furnace provided with a hydrogen atmosphere and subjected to a temperature of-about one and one-half hours. After sintering, the briquette is coated with a thin film of zinc stearate by dipping in a solution containing about one part zinc stearate dissolved in about 20 parts carbon tetrachloride at room temperature and the carbon tetrachloride evaporated from the surface of the briquette.

The lubricated briquette is compressed and shaped to the dimensions of a caliber .30 projectile while confined in cavity 7 of two piece shaping die block 9 by plunger 6 shown in Figure 2. A final pressure of about 75 tons per square inch is reached in this operation after which the briquette is removed from the die block 9 by separating the two parts thereof and is returned to the furnace having the hydrogen atmosphere and heated at about 1100 C. for about one-half hour. After cooling to about room temperature, the briquette is forced through a conventional type projectile sizing die, the lubricant is removed therefrom by washing with solvent or heating in a furnace to effect evaporation thereof, and a chamfer 10 shown in Figure 3 is formed at the juncture between the base and side of the projectile in a conventional machine to facilitate assembly with the cartridge case. The density of the finished projectile will be about 7.7 grams per milliliter.

In another embodiment of this invention, the process described in the foregoing embodiment is followed with the only exceptions being changes in granulation of the iron shot and type of powdered iron used. The particle size of the iron shot is less than about 1650 microns with about 50% by weight of the particles Within the range of about 830 microns to about 1650 microns, about 35% between about 550 microns and 830 microns and 15% within the range of about 300 microns to 550 microns particle size. The iron shot is coated with an iron powder which was produced by the chemical reduction of iron oxide and has a particle size of less than about 44 microns. The density of the caliber .30 projectiles made in accordance with this embodiment is about 7.7 grams per milliliter.

As illustrated in Figure l of the drawing, the cavity formed in die 4 is shaped to form a compact substantially cylindrical over the greater part of its length but with a nose portion of two diameters similar to two superimposed truncated cone portions 11 and 12' in plungerr2. Compacts formed in this die are sintered and the resulting briquettes shaped into projectiles in die 9 of Figure 2 and again sintered.' Dies having such a construction are advantageous in producing relatively non-porous briquettesfor the purpose and facilitate ejection'of the compact from plunger 2; If desired, the size of the iron shot of the foregoing embodiments can be varied such that smaller shot is used for forming the nose portion of the compact than is used for forming the cylindrical portion thereof. In addition to the variations in amounts of comparatively large iron particles and amounts of smaller iron particles and other possible variations pointed out hereinbefore, other changes can be made in the foregoing detailed description of this invention. For instance, microcrystalline waves, ceresin or the like can be substituted for the paraffin; other solvents such as naphtha or other chlorinated solvents can replace the carbon tetrachloride; and stearic acid, metallic stearates or synthetic powdered adhesives and the like can be utilized to replace the solid hydrogenated cottonseed oil in the binder utilized in forming the coating of smaller particles of iron on the comparatively larger particles. Some variation in pressure is permissible in each pressing operation although the pressure must be suificient to produce the substantially non-porous briquette of this invention. Pressure ranges in the first pressing operation can vary from about 30 tons per square inch to about 50 tons per square inch while best results are obtained if the pressure of the second pressing operation is within the range of about 50 to 75 tons per square inch. In addition, the temperature of the sintering operation can vary from about 1000 to about 1200 C. and the time at the temperature from about three-fourths hour to about two hours or more. The annealing treatment after the second pressing of the briquette can vary from about 1000 C. to about 1200 C. for from about one-half hour to about one and one-half hours or more.

This invention also contemplates rust-proofing briquettes such as projectiles, if desired, by methods such as for example, by applying a film of resinous material, parafiin, ozokerite, ceresin or any other type of wax or wax formulation, by providing a copper or similar plating on the surface thereof or other suitable rustproofing process.

This invention accordingly accomplishes its objects and provides a novel method for making briquettes having novel properties from particles of iron.

Numerous other changes and modifications of the embodiments of this invention herein described will become apparent to those skilled in the art which can be made Without departing from the spirit and scope of this invention.

Having thus described the invention what is claimed and desired to secure by Letters Patent is:

1. As a new and improved article of manufacture made from iron particles, a compressed and sintered mass composed essentially of substantially spherical particles of iron having a diameter of not less than about 300 microns and a Diamond Pyramid hardness of not more than about 220, and smaller particles of iron powder, said mass having a density substantially equal to the density of pure iron and having a rust proofed surface composed of surfaces of said spherical particles and said smaller particles of iron.

2. As a new and improved article of manufacture made from iron particles, a compressed and sintered mass composed essentially of substantially spherical particles of iron having a diameter of not less than about 300 microns 6 and a Diamond Pyramid hardness of not. more than about 220, and smaller particles of iron, said mass having a density substantially equal to the density of pure iron and having a surface composed of surfaces of said spherical particles and said smaller particles of iron.

3. As a new and improved article of manufacture made from iron particles, a compressed and sintered mass composed essentially of substantially spherical particles of iron having a diameter of not less than about 300 microns and a Diamond Pyramid hardware of not more than about 220, and particles of iron powder having dimensions of less than about 80 microns, said mass having a density substantially equal tothe density of pure iron and having a surface composed of surfaces of said spherical particles and said smaller particles of iron.

4. As a new article of manufacture made from iron particles, a projectile for ammunition cartridges composed essentially of compressed and sintered substantially spherical particles of iron having a diameter of not less than about 300 microns and a Diamond Pyramid hardness of not more than about 220 and smaller particles of iron powder, said projectile having a density substantially equal to the density of pure iron and having a heterogeneous surface composed of the surfaces of said spherical particles and said smaller particles of iron which is adapted to be indented by the n'fling of a steel gun barrel as the projectile is propelled therethrough.

5. The projectile of claim 4 composed of from about to about parts smooth surfaced spheres and from about 40 to about 20 parts iron powder.

6. The method for making substantially non-porous projectiles for ammunition cartridges from particles of iron which comprises mixing substantially spherical particles of iron having a diameter not substantially less than 300 microns with particles of iron having lesser dimensions while wet with a binder and until the smaller particles have formed a coating on the larger particles, pressing the resulting agglomerate in a die into a generally cylindrical shape but terminating at one end in a generally truncated conical shape, sintering the resulting compact until the iron particles are welded together and until substantially all of the binder has been removed, pressing the resulting briquette and simultaneously shaping it into a generally cylindrical shape having an ogive at one end thereof, and again sintering in a reducing atmosphere.

References Cited in the file of this patent UNITED STATES PATENTS 2,342,799 Goetzel Feb. 29, 1944 2,401,483 Hensel June 4, 1946 2,409,307 Patch Oct. 15, 1946 2,411,379 Langhammer Nov. 19, 1946 OTHER REFERENCES Powder Metallurgy, by Goetzel, volume 1, 1949, Interscience Publishers, pp. 87, 96, 249 particularly of interest.

Selected Government Research Reports, vol. 9, Powder Metallurgy, issued by the Ministry of Supply, London, England, 1951, pp. 53, 54, 59, 61, and 86 especially relied on. 

1. AS A NEW AND IMPROVED ARTICLE OF MANUFACTURE MADE FROM IRON PARTICLES, A COMPRESSED AND SINTERED MASS COMPOSED ESSENTIALLY OF SULBSTANTIALLY SPHERICAL PARTICLES OF IRON HAVING A DIAMETER OF NOT LESS THAN ABOUT 300 MICRONS AND A DIAMOND PYRAMID HARDNESS OF NOT MORE THAN ABOUT 220, AND SMALLER PARTICLES OF IRON POWDER, SAID MASS HAVING A DENSITY SUBSTANTIALLY EQUAL TO THE DENSITY OF PURE IRON AND HAVING A RUST PROOFED SURFACE COMPOSED OF SURFACES OF SAID SPHERICAL PARTICLES AND SAID SMALLER PARTICLES OF IRON. 